Fuel cells are useful for generating electrical energy based on an electrochemical reaction. Different types of fuel cells have been developed. Phosphoric acid fuel cells (PAFCs) utilize a phosphoric acid electrolyte between cathode and anode electrodes. Polymer electrolyte membrane (PEM) fuel cells utilize a polymer electrolyte between the electrodes. Each type of fuel cell has its own characteristics, which may make it more suitable for a particular application.
In PAFCs, the phosphoric acid electrolyte is retained in a matrix that is situated between the electrodes. Different materials have been used for the matrix layer. U.S. Pat. No. 3,694,310 describes a phenolic resin matrix layer. One drawback associated with phenolic resin matrix layers is that over time a reaction between the phosphoric acid and the organic material of the matrix layer at elevated temperatures produces a molecule that adsorbs onto the electrode catalyst and poisons the catalyst. As a result, the performance of the fuel cell degrades.
U.S. Pat. No. 4,017,664 describes a matrix layer made of silicon carbide. One drawback associated with such a matrix layer is that the oxide on silicon carbide slowly dissolves during typical fuel cell operating conditions and converts to silicon phosphate, which is insoluble in phosphoric acid. This causes an associated loss of phosphoric acid electrolyte and the insoluble phosphate material could potentially block fuel or oxidant gas delivery to the electrodes.
It would be useful to have a PAFC matrix layer with improved characteristics compared to previously proposed or used matrix layers.